P_D components and distractor inhibition in visual search: New evidence for the signal suppression hypothesis

Drisdelle, Brandi Lee; Eimer, Martin · 2021 · Crossref

DOI: 10.1111/psyp.13878

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Summary

This study investigates the debate over whether salient, task-irrelevant distractors automatically capture attention or are actively suppressed. Specifically, it addresses conflicting interpretations of the PD component, an electrophysiological marker previously linked to distractor inhibition. While Gaspelin and Luck (2018a) argued the PD reflects active signal suppression, Kerzel and Burra (2020) challenged this, proposing a "lateral-first serial scanning" hypothesis. They suggested the PD is actually an N2pc component reflecting attentional deployment to lateral context items, followed by a contralateral negativity indicating capture by the distractor. The current research tests this alternative account by determining if the PD persists when lateral locations are entirely task-irrelevant, a condition where serial scanning of lateral items would be unnecessary. The researchers employed an event-related potential (ERP) study with 18 participants performing a visual search task. Displays contained four items: two on the vertical midline and two on the horizontal midline. Participants searched for a shape-defined target while ignoring a salient color singleton distractor. The experimental design manipulated attentional focus across three blocked conditions: unfocused attention (targets could appear anywhere), focused attention on the midline (targets only on the vertical axis), and focused attention on lateral positions. This design allowed the authors to isolate whether the PD component elicited by lateral singletons depended on the potential task relevance of lateral locations. EEG data were recorded, and lateralized ERP components were analyzed by subtracting ipsilateral from contralateral activity to isolate the PD (positivity) and N2pc (negativity). The results demonstrated that lateral color singletons elicited a significant PD component in both the unfocused attention condition and the focused attention [midline] condition, where lateral locations were completely irrelevant. This finding contradicts the serial scanning hypothesis, which predicted the PD would only appear when lateral items were potential targets. Although the PD amplitude was larger in the unfocused condition, additional analyses comparing unfocused and focused [lateral] conditions revealed that PD magnitude was driven by the task relevance of the distractor’s location rather than the total number of attended locations. Furthermore, the PD onset was significantly earlier than the N2pc onset for targets, indicating suppression occurs prior to attentional allocation. The contralateral negativity following the PD was interpreted as a second PD elicited by non-salient distractors on the opposite side, rather than an N2pc indicating capture. These findings provide strong evidence for the signal suppression hypothesis, confirming that the PD component reflects the active inhibition of salient distractors rather than attentional selection of context items. The study reconciles previous conflicting results by demonstrating that distractor suppression is a proactive process that scales with the potential interference of the distractor. This supports the view that attentional control mechanisms can suppress stimulus-driven saliency signals to prevent capture, even when those signals are pre-attentively registered.

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Topics

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• visual search
• attention selective divided